Numerous industrial activities exist in the field of reforming flat glass sheets. Currently, these activities are mostly for making shaped glass articles for automotive applications, e.g., windshields and side windows, and architectural applications, e.g., curved glass for architectural and commercial non-electronic displays. Reforming processes for these applications are typically characterized by limited glass deformation, curvatures with large radii (usually greater than 50 mm), and large glass sheet thicknesses (usually greater than 1.5 mm).
Reforming processes based on gravity sagging are known in the current art. See, e.g., U.S. Pat. No. 6,240,746 B1, “Glass plate bending method and apparatus,” 5 Jun. 2001 [1]. In gravity sagging, the glass sheet is positioned on a ring or skeleton that supports the periphery of the glass sheet. The system is then heated to a temperature close to the softening point of the glass. Under gravity, the glass sags, eventually assuming the desired shape. Differential heating of some regions of the glass sheet can be used to obtain some final shapes that cannot be reached solely by isothermal gravity sagging. For some special shapes, more advanced techniques have been developed that are based on articulated skeletons (see, e.g., U.S. Pat. No. 4,286,980 A, “Method and apparatus for forming bent plate glass,” 1 Sep. 1981 [2] and U.S. Pat. No. 5,167,689, “Process for bending glass sheets,” 1 Dec. 1992 [3]). The idea is to have the skeleton articulated so that at some point during the gravity sagging process the outer shape of the supporting frame is modified to eventually obtain a more complex design, for example, a smaller local radius of curvature.
Reforming processes based on press bending are known in the art. See, e.g., U.S. Pat. No. 6,422,040, “Method for forming glass sheets” [4] and WO 2004 087590 A2, “Method for crowning sheets of glass by pressing and suction,” 14 Oct. 2004 [5]. In press bending, the glass sheet is shaped by contact with a central male mold, with an external female mold pressing the periphery of the glass to the central male mold. This process has the ability to obtain curvatures with relatively small radii, e.g., as small as 10 mm (see, ref. [5] above), and relatively complex shapes.
Nowadays, interest is growing in high-quality, thin-walled, shaped glass articles, and in particular shaped glass articles having a combination of flat area(s) and bent area(s), the bent area(s) typically having highly curved shapes. These complex shaped glass articles are desired for use as glass covers or doors or windows in portable electronic devices, such as tablets and smart phones, and larger smart appliances, such as television sets and refrigerators. These newer applications generally have the following requirements for shaped glass articles: curvatures with small radii, e.g., less than 20 mm, in the bent area(s), almost perfect flatness and optical quality in the flat area(s), bent area(s) that may be located very close to the outermost edge of the glass, and bend angle that can be greater than 90 degrees. These requirements are difficult to achieve using reforming processes such as described above.